To get into Boston from Braintree is about 20 minutes by car and 40 minutes by train from Braintree station on the red line.
Downtown Boston? If so, it takes a little under 20 min if there's not much traffic
... but there's always traffic. Give yourself 30 min to be on the safe side
Like others have mentioned, 20- 50 minutes. It really depends. Weekdays, mid day and nights I would say 30 minutes. Rush hour 40-50. There is a lot of construction on the red line near Quincy and on Longfellow bridge that slows the commute down considerably at the moment. Also trains have been breaking down frequently leading to delays. Either way I would try to leave 20 minutes early incase there are issues.
If you're talking about rush hour in the morning, it could take 30 to 40 minutes using the HOV lane you must have two people in the vehicle.
Thanks! Your answer is awaiting moderation.